The present invention relates to a liquid filtering device, and more particularly to a liquid filtering device for filtering out leukocytes and other components from blood and extracting red cells only to produce concentrated red cells.
Filtering devices are employed to filter a liquid to obtain a necessary component from the liquid. In order to achieve satisfactory separation performance and stabilize liquid processing capability, it is desired that any clogging of the filter element of the filtering device be minimized. To effect component transfusion on a patient who needs only red cells, for example, it is customary to obtain concentrated red cells through a centrifugal separation process, and the produced concentrated red cells are administered to the patient. Since the solution containing concentrated red cells also contains many leukocytes and platelets, it is not preferable to transfuse this solution to the patient who needs only red cells.
There has been employed a filtering process for increasing the purity of concentrated red cells (a red cell preparation) by removing leukocytes and platelets. The filtering process uses a main filter element for filtering out leukocytes and platelets and a preliminary filter element which has a smaller apparent density and a lower filtration resistance than the main filter element in order to reduce clogging in the main filter element.
One conventional liquid filtering device for producing highly pure red cell preparations is shown in FIG. 1 of the accompanying drawings. The liquid filtering device has a housing 2 in the form of a flat plate which defines a space 4 therein that is centrally divided by a partition plate 6 disposed in the housing 2. The partition plate 6 has a liquid inlet port 8 defined in an upper end thereof, and a liquid outlet port 10 defined in a lower end thereof. First filter elements 12a, 12b be applied to the partition plate 6 in sandwiching relation thereto, and second filter elements 14a, 14b are placed over the first filter elements 12a, 12b, respectively. The second filter elements 14a, 14b are pressed against the first filter elements 12a, 12b, respectively, by a plurality of projections 16 on inner wall surfaces of the housing 2.
The first filter elements 12a, 12b serve as preliminary filter elements for minimizing clogging in the second filter elements 14a, 14b. Therefore, the first filter elements 12a, 12b are coarser than the second filter elements 14a, 14b, and are made of nonwoven fabric of polyester, nylon, or the like which has a smaller apparent density than the second filter elements 14a, 14b.
The second filter elements 14a, 14b have a larger filtration resistance than the first filter elements 12a, 12b. Preferably, the second filter elements 14a, 14b are made of a porous material such as of synthetic resin or a nonwoven fabric of ultrathin fibers. In the conventional filtering device shown in FIG. 1, however, the first filter elements 12a, 12b and the second filter elements 14a, 14b are merely pressed against each other in superposed relation and fixedly positioned in the housing 2. During a filtering process, a liquid to be filtered, typically blood, may flow between the pressed regions of the first filter elements 12a, 12b and the second filter elements 14a, 14b, a phenomenon known as "short pass", and may directly go unfiltered into the liquid outlet port 10. Thus, the liquid is not effectively filtered by the second filter elements 14a, 14b. As a result, the ratio or percentage of removed leukocytes, i.e., the leukocyte removal ratio, is lowered. When the filtration resistance of the second filter elements 14a, 14b is increased by clogging, the first filter elements 12a, 12 b are liable to be separated from the partition 6, and the liquid which is not filtered at all may be directed toward the liquid outlet port 10. Consequently, the conventional liquid filtering device has proven unsatisfactory.